Method of producing substantially pure metallic magnesium directly by electrolysis of a fused bath



Patented Aug. 25, 1931 UNITED STATES P'A'TENTi oFF cr.

RALPH I. HUNTER, OF MIDLAND, MICHIGAN, ASSIGNOB T THE'DOW CHEMICAL CO!-PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN .EETHOD OFPRODUCING SUBSTANTIALLY PURE METALLIC @MAGN ESIUM DIRECTLY A BYELECTBOLY SIS OF A FUSE!) BATH Io Drawing.

The present invention relates to the production of metallic magnesium bythe electrolysisof a fused bath containing magnesium chloride.

An object of the invention is to separate the metal directly from thebath in a sufficiently pure condition to enable its use in the artswithout further refining.

It has been considered necessary and has been the practice heretofore,so far as I am aware, to subject metallic magnesium produced in theelectrolytic process to a subse-'- quent refining procedure. Variousmodes of such procedure have been used or proposed.

One of the least costly procedures is to remelt the crude metal in thepresence of a limited amount of a suitable flux with which it is thenagitated, said flux being of a character to coat the surface of themetal ex posed to the air so as to protect it from oxidation. After aperiod of such washing, the

basic magnesium compounds present in the 1 r'aw metal are largely washedout and transferred to the flux whereupon the metal may i be dipped or"otherwise separated from the flux and cast into ingots or disposed of asdesired. 7

Such practice requires arehandling and rem'elting of the metal andprovision of associated plant and apparatus for the refining step. I

I have invented a method of producing Jhe equivalent of the so refinedmetal directly in the electrolytic cell whereby such rel andling',remelting and plantcosts are saved.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the method hereinafter fully described andparticularly pointed out in the claims, the following descriptionsetting forth in detail one mode of carrying out the invention, suchdisclosed mode illustrating, however, but one of various ways in zsliphthe principle of the invention may be scribed.

Application filed Kay 31, 1929. serial in. 867,251.

4 I electrolyze a suitable fused bath contain-' ing magnesium chlorideand sodium chloride. The exact composition of the bath appears to beunimportant. Any bath suited to liberate magnesium upon electrolyzingwill serve as a washing agent in my process, as hereinafter described. Iprefer to use for the electrolysis a type of cell in which the liberatedmetal floats upon the bath, I prefer in any event a type of cell inwhich the metal is gathered together .into a compact molten mass. Suchan electrolytic cell is disclosed in co-pending application SerialNumber 210,785 by Louis E. Ward and the applicant herein. In the celltherein described the metal is automaticall led into a gathering orcollecting well. ther forms of construction than therein disclosed mayobviously be employed, and it is further obvious that in some such, thecollecting well or zone may be at one, side or one end, i. e. along themargin of the fused bath, thereby permi ing. easy access for theoperations hereig aften de-y' v I permit the metal to collect in suchwell by the gathering together of the separate globules of metal preerably under restricted contact with the air or in an atmosphere ofhydrogen, if the metal be floating upon the bath, which latter gas mayaccompany the metal'liberated due to the presence of water or basicchloride in the chloride fed to the bath. After the metal has collectedto a substantial depth, which may be several inches, I find that it hasacquired a -consistent character, the separate globules having coalescedand squeezed out the bathor flux. I agitate or mix it with the cell bathwhich may be readily done by removing the cover above the metal, if onebe used, insert- 4 ing a ladle, dipping and pouring the metal over andover whereby it is contacted with the bath. Mechanical a 'tating meansmay, however, be employed, riven by power, if 00 desired, to impartrelative motion to the bath and the metal whereby freshsurfaces of metalare brought successively into contact with the bath. After a'shortperiod of such washing I withdraw the metal and cast it into molds. Thismay be done by ladling or other procedure convenient or desirable. Ifind the metal so treated before withdrawing from the cell to havesubstantially the same" degree of purit as the metal heretofore producedby with rawing from the bath without such treatment, casting into crudeingots, subsequently remelting, washing with a flux and again castinginto ingots. The metal may be obtained by means of my simplifiedprocedure with a purity of 99.85 per cent or better.

The impurities in the metal are washed out by the bath, and inasmuch assuch in crement of impurity in the bath is a small one, substantiall noadditional burden is placed upon the redging of the sludge from .thecell incident to its normal operation.

.Much effort has been directed to the development of thetechnicaldetailsof after refining, i.-e. remelting in a refining flux. The fused bath,which is used in the cell, may or may nothave the ideal compositionindicated by such research. I find, however, that equivalent results arereadily and cheaply obtained emplo g the cell bath itself as refiningflux. fter refining usually has been done by washing the remelted .metalwith a quite limited weight of flux,

whereas in my method I wash it with a relatively very large weight offlux. The use of flux to the extent of one-half (.or less) the weight ofmetal is a customary ratio for after refining. In my method the weightof the flux or bath relative to the metal may be several hundred timesthat of thelattcr. The dredging of the sediment is a normal operation inthe electrolytic step which pro 'cedure keeps the bath effectively cleanand active as a washing agent for the metal. The advantage of a largeratio of flux to metal appears to outweigh any disadvantage which may beinherent in the. bath composition relative to an ideal compositionthereof.

- In after refining the bathbeing small from to" percent dependin uponthe type of'cell used. I find that i the metal I be gathered into a areato a substantial. .depth enablingit to aggregate into the bath.

a consistent mass and be then washed, as herein described, thepurification is unexpectedly improved and ametalin excess of 99 percentpure is readily obtained.

I find further that practicing washing upon such an aggregated mass ofmetal there results a prompt and effective separation of the metal fromthe flux and that the withdrawal of the metal from the cell with aminimum amount of flux, is easily done the total impurity including theflux being less than one percent of the total withdrawn.

Although my method of producing a substantially pure metal is morereadily applicable when employed in large scale wor ing i. c. withelectrolytic cells using current in excess of 10,000 amperes, it may beemployed in small scale production with advantage.

It is obvious that myvimproved method eliminates the requirement forseparate melting pots, furnaces and associated e uipment incident to andconnected with a er refining. It saves the cost of rehandl ng, labor andfuel for reinelting. It also consolidates the production and refiningsteps at one'point in one vessel regllnring a minimum of supervision,labor, el and equipment and hence constitutes a valuable ad- Vance inthe art.

Other modes of applyin the principle of my invention may be emp oyedinstead of the one explained, change bein made as regards the methodherein disc osed, provided the step or steps stated by any of thefollowing claims or 'the equivalent of suc stated step or steps beemployed.

I therefore particularly point out and distinctly claim as my invent1on:

1. In a method of the character described, the step which consists inwashing molten metallic magnesium with the fused bath containingmagnesium chloride from which it has been liberated byelectrol sisbefore removal of said metal from said ath.

2. In a method of the character described, the steps which consist inelectrolyzin a fused bath containing magnesium chloride, gatheringtogether the globules of the liberated metal into a consistent masssubstantially free from inclusionsof bath, agitating andwashing the sogathered metal with the bath and removing the purified metal fromthe'bath. 1

3. In a method of the character described, the steps which consist inelectrolyzing a fused bath containing magnesium chloride underconditions permitting the liberated nietal to float thereon, gatheringthe liberated metal into a consis nt mass floating on said bath,agitating a (1 Washing the so collected metal with [the bath upon whichit floats and removing the purified metal from 4. In a method of asubstantially pure magnesium metal by electrolysis of a fused bathcontaining magnesmm chloride, the steps which consist in gatheringtogether the globules of metal so liberated into a consistent masssubstantially free from inclusion of bath and then setting up relativemotion between said gathered metal and the bath whereby fresh surfacesof the metal are brought successively into contact with the bath.

Signed by me this 28th day of May, 1929.

RALPH M. HUNTER.

